Pneumatic-hydraulic fluidic transducer



United States Patent 3,457,847 7/1969 Furlong..... 3,457,937 7/1969 Rainer ABSTRACT: A fluidic transducer having no moving mechanical parts utilizes a two stage fluid amplifier circuit for converting pressurized pneumatic signals to a hydraulic output, or vice versa. A variable fluidic resistance means connected in bridge circuit relationship between the first and second stage amplifiers provides a hydraulic-pneumatic interface therebetween and is comprised of two fluid amplifiers utilizing only the power fluid and control fluid inlets thereof. The outputs of the first stage amplifier are connected to single control fluid inlets of the intermediate fluid amplifiers for controlling the downstream pressure of the power jets therein. The control fluid inlets of the second stage amplifier are connected to the power fluid inlets of the intermediate fluid amplifiers such that a control signal applied to the first stage amplifier causes proportional changes in the downstream pressure of the power jets of the intermediate amplifiers which are reflected into the control fluid inlets of the second stage amplifier.

Patented 0a. 20, 1910 3,534,159

[)7 ven t or: Thomas "5. Honda.

Myinvention relatesto a pneumatic-hydraulic transducer having no moving mechanical parts; and in particular, to a transducer utilizing analog-type fluid amplifiers in abridge circuit connection to obtain the'desired interface between the pneumatic and hydraulic portions of the device.

, Pneumatic-hydraulic transducers are'usefulzin many control 7 systems 'wherein'one of the signals is of the pressurized pneumatic or hydraulic type and'a particularcircuit in thesyste'm utilizes the opposite typefluid signal for processing thereof. Such transducers are especially'useful in,-but not limited to.

systems and circuits employing the recently' 'developed fluid I control devices known as fluid-amplifiers;

Prior art pneumatichydraulic-transducers utilize. a conven-- tional analog-type fluid amplifier provided witha hydraulic fluid power supply and pneumatic control signals for accomplishing the hydraulic-pneumaticinterface. Such prior art approach necessarily results 1 in entrainment of thepneumatic medium in the hydraulic fluid therebygenerating a noise due to the mixing process. Other types-of prior art pneumatichydraulic transducers utilize moving mechanicalparts which are subject to wean. fatigue failure; friction and hysteresis.

7 Thus, there is a need for providing a pneumatic-hydraulic transducer having no moving'mechanical parts'and capable of isolating any noise generated by" mixing "pneumatic and hydraulic'fluids from the output of the'tran'sducert.

Therefore; one of theprincipal'objects of my invention is to provide a fluidic-type pneumatic-hydraulic transducer having no moving mechanicalparts;

Another object of my'inventio'n'is to'provide such transducer wherein the mixing of the"pneumaticand hydraulic fluids and noise generatedthereby is isolated from the output of the transducer.

A further object of my invention is'to construct the transducer from a bridge circuitarrangementof'fluid-ampIifiers wherei'n two'of the fluid amplifiersfunction' as variable fluidic resistances. I

Briefly stated, in meeting theobjects of my invention 1 providea two stage fluidic amplifier circuit wherein the first stage is an analog-type fluid amplifier-provided witha powerfluid supply and control fluid'signal of a first type; fluid which may be pneumatic or hydraulic';and-.a' second stage: analog-type fluid amplifier provided with a power'fluid supply andcontrol fluid signal of a second typefluid opposite from that in the first stage. Variable fluidic resistance means-are connected in bridge'.circuit relationship between-the first andsecond stage amplifiers for providing :a pneumatic-hydraulic interface therebetween. The variable fluidi c resistances means comprise two analog-type fluid amplifiers each having a first control fluid inlet connected to an output ofthe first stage amplifier and the second control fluid inlets being iblocked. The power flu'id supply for the variabl'e'fluidic resistance fluid amplifiers' is commonwith thecontrolfluid supplied to thesecond 4 stage amplifier whereby changes in the :downstream pressure of the power'jets in the variable resistance fluid am-- plifiers' are reflected into thecontrol fluidinlets of the second stage amplifier to'the rebyconvert thefirst' type'fluidcontrol signal in the first stage. amplifie'r-to a control 'signaiof the second type fluid in the second stage amplifie'r'witho'ut the use of any moving mechanical parts and providing'isolation of=any mixing of the two fluids from, the control fluid-inlets of the second stage.

The' features of my-invention' which I desire to protect herein' are pointed out -with-'particularity in the appended claims. The invention itself, however both'as to its organization and methodof operationytogether with further -objects and advantages thereof may' best be understood by reference to the following description taken in connection withthe accompanying drawings wherein'like parts ineach of the several FIGS. are identified bythe same reference character and wherein:

FlG. his a plan view ofa pneumatic-hydraulictransducer constructed in accordance withmy invention;

FlG. lb is a schematic representation of the transducer Referring now in particular to FIGS. la and 1b; there are shown conventional fluid amplifiers of the analog (proportional) type designated as a whole by numerals l0 and 1.1 which comprise the first or input stage and the second or output stage, respectively, of my fluidic transducer. Each 'ofxfl'uid amplifiers 10 and "T1 is' provided with a power fluid inlet terminating" in a fluid flow restrictor or nozzle'llfor generating a power jet of fluid upon the inlet being supplied with a .pressurized fluid. A pair of fluid receivers l3jaridil4 are disposed downstream of the power fluid nozzle 12 for receiving at least a part of the fluid from the power jet. lntermediate the power nozzle and receivers are a pair of control fluid inlets terminating in opposed fluid flow'restrictors or nozzles 15 and 1:6 for deflecting the power jet in proportion to the magnitude of the differential pressure of the fluid supplied to the control fluid inlets. lntermediate the control nozzles and receivers are disposed a pair of side vent passages 17 and 18 havingtheir outer ends open to the atmosphere or returned to a sump dependingupon the particular fluid suppliedt'o the amplifier. A center vent passage 19 is also provided intermediate the receivers.

A first type pressurized fluid which may be pneumatic (any suitable gas including air) or hydraulic (any suitable liquid including oil or water) is supplied to the first stage amplifier 10. Thus. the pressurized power fluid supply Ps, and the differentially pressurized .input control'fluid-signal APc are each of the first type fluid. As a resultj t he differentially pressurized output of the first stage AP. obtained between receivers 13 and 14 is also of thefirst type fluid.

The second stage fluid amplifier 11 is provided with a power fluid supply P5 and control fluid signal APc, of a second type fluid .which is opposite from that in the first stage amplifier. Thus, if the fluid supplied to the first stageamplifier is pneumatic, the fluid supplied to the second stage is hydraulic. and vice versa. I

Variable fluidic resistance means indicated as 'a whole by numerals 20 and Zl are connected in bridge circuit relationship between the first stage and second stage fluid amplifiers l0 and ll for providing a hydraulic-pneumatic interface therebetween having no moving mechanical parts. The variable fluidic resistance means 20, 21, comprise what may be described as halves of two identical analog-type fluid amplifiers of the same type as amplifierslo and 1!. In particular,

the variable fluidic resistance means 20 and 21 each comprise a power fluid inlet terminating in a power fluid nozzle 12a and connected to'the control fluid inlet terminating in nozzle 15a' of half amplifier 20"by means of a suitable fluid flow passage 23. ln like manner, the output of fluid receiver 14 is connected to the control fluid inlet'terminating in nozzle 15a of haif amplifier 2l-by means of fluid'flow passage 24. The control fluid inlets terminating in nozzles 16a of half amplifiers 20 ,and 21 are each blocked such that no control fluid issues from nozzles 16a. Finally, the power fluid inlets of half amplifiers 20; and 21 are connected to power fluidsupply Ps, through fluid flow restrictors 25 comprising narrow passages providing equal predetermined fluid flow resistance values, and are directly connected to the control fluid inlets of the secondjstage amplifier by means of. fluid flow passages 26 and 27. The power fluid inlet of the second stage amplifier 11 is also connected to the power fluid supply Ps but without the intermediate fluid flow restrictors 25 therebetween.

The operation of my fluidic transducer may be described as follows. Assume that the first type fluid supplied to the input stage amplifier 10 is a hydraulic fluid comprising pressurized water. Thus, water at a substantially constant pressure above ambient is supplied from power fluid source Ps to the power fluid inlet of input amplifier 10 for generating a liquid jet issuing from nozzle 12 in the direction of receivers 13 and 14. The input control fluid signal APc supplied to the transducer is a differentially pressurized (water) signal applied to the control fluid inlets of input amplifier 10. A differentially pressurized (water) output AP appears across the two receivers 13, 14 of input stage amplifier l and is transmitted by means of passages 23 and 24 to the control fluid inlets terminating in nozzles 15a of half amplifiers 20 and 2]. Assuming the general case wherein the input control signal APc, has a differential pressure magnitude other than zero, the pressures of the (water) signal in passages 23 and 24 are unequal. It is further assumed that the second type fluid supplied to the output stage 11 is a pneumatic fluid comprising pressurized air. Thus, air at a substantially constant pressure above ambient is supplied from power fluid source Ps to the power fluid inlet of output amplifier l1, and such air at a reduced pressure due to resistors 25 is also supplied to the power fluid inlets of the intermediate amplifiers 20 and 21. The unequal hydraulic (water) pressures in passages 23 and 24 result in control fluid (water) jets of unequal pressures issuing from nozzles 15a in the half amplifiers 20 and 21. The unequally pressurized hydraulic control jets in half amplifiers 20 and 21 cause unequal control of the downstream pressure of the pneumatic (air) power fluid jets therein and such unequal power fluid pressures are reflected into the control fluid inlets of the output stage fluid amplifier 11, developing a differentially pressurized pneumatic control signal APc thereat. Pneumatic control signal APc causes a differentially pressurized pneumatic output APo between receivers 13, 14 of output stage amplifier 11 having a magnitude directly proportional to the magnitude of the differentially pressurized hydraulic input control signal APc applied to the input stage amplifier l0 and substantially linearly proportional therewith over a particular range of input control signal pressures. The effect produced by the. half amplifiers is thus that of a variable fluidic resistance means.

' In the special case wherein the input control signal APc has a differential pressure magnitude of zero, the pressures in passages '23 and 24 are equal, resulting in equal power fluid pressures reflected into the control fluid inlets of output stage amplifier 1], and a differential pressure magnitude of zero at the output AP thereof.

The selection of proper pressure relationships prevents the undesired introduction or mixing of one of the fluid mediums into the portion of the circuit containing the other fluid medium. Thus, the relationship of power fluid supply pressures Ps andPs and the resistance value of fluidic resistors 25 are selected to prevent the mixing of the first fluid medium confined to thecircuit defined by first stage amplifier and the generally of pressure magnitude less than the second stage supply pressure PS2 whether the transducer converts hydraulic-to-pnuematic, or pneumatic-to-hydraulic. Resistors 25 haveiequal resistance values sufficiently high to prevent control signal attenuation.

Resistors 25 also determine the overall gain of my transducer as defined by the ration 2 The resistance value of resistors 25 is selected to provide a power fluid supply pressure to half amplifiers 20 and 21 which is in the range of 0 to 0.40 Ps The maximum resistance value 0bviously provides a minimum power fluid pressure to half amplifiers 20 and 21, and resultant maximum 'gain of the transimum output A1 minimum gain of the transducer, and noise and stability proble'rnsassociated with the output stage 11. Thus, the resistance value of resistors 25 is selected to obtain a predetermined suff ciently high gain and saturation limit for the transducer and" mixing of the fluid mediums is also prevented in the inplit and output stages.

FIG. 2 illustrates'the input-output characteristics of my transducer when employed, as hereinabovedescribed, as a hydraulic-to-pneumatic transducer wherein the abscissa represents the differentially pressurized hydraulic input control signal Al 'c plotted in p.s.i. and the ordinate represents the differentially pressurized pneumatic output AP in psi. The particular characteristics illustrated in FIG. 2 were obtained for a hydraulic (water) supply pressure Ps, of 4 psi. and a pneumatic (air) supply pressure Ps of 5 psi.

FIG. 3 illustrates the input-output characteristics of my transducer when employed as a pneumatic;t'o-hydraulic transducer of interface circuit for two values (Sand 10 p.s.i.) of hydraulic (water) supply pressure PS2 and 'a pneumatic (air) supply pressure Ps of4 p.s.i. In this figure. the ordinate is also plotted in p.s.i,, but the abscissa is in inches of water. It would be expected that, in general, the gain of my transducer when employed as a hydraulicto-pneumatic transducer is higher than when employed as a pneumatic-to-hydraulic transducer due to the higher density of the hydraulic control fluid impinging on the pneumatic power jet in the half amplifiers.

From the foregoing description, it can be appreciated that my invention makes available a fluidic transducer or interface having no moving mechanical parts and which is adapted for converting pressurized signals of one type fluid medium to a pressurized output of a second type fluid medium wherein the two type mediums are of the pneumatic and hydraulic type. The transducer comprises two stages of analog-type fluid amplifiers and variable fluidic resistance means connected in bridge circuit relationship therebetwecn. The variable fluidic resistance means comprise the input elements of two fluid amplifiers of the analog-type. Proper selection of the power fluid supply pressures to the four amplifiers prevents a mixing of the two fluid mediums in either the input or output amplifier stages. The avoidance of mixing of the two fluids prevents the generation of noise produced bysuch mixing and thus provides a high performance transducer compared to conventional pneumatic-hydraulic transducers. My transducer is equally capable of operation as a pneumatic-to-hydraulic transducer and a hydraulic-to-pneumatic transducer.

Having described a preferred embodiment of my fluidic transducer, my invention is defined by the following claims.

lclaim:

l. A fluidic transducer for converting pressurized pneumatic signals to pressurized hydraulic signals, or hydraulic to pneumatic, without the use of moving mechanical parts comprising: I r

a first stage analog-type fluid amplifier provided with a power fluid supply and control fluid signal of a first type fluid which may be pneumatic or hydraulic;

a second stage analog-type fluid amplifier provided with a power fluid supply and control fluid signal of a second type fluid which may be hydraulic or pneumatic, and being the opposite type fluid from that in said first stage amplifier; and

variable fluidic resistance meansconnected in fluid circuit relationship between said.first stage and second stage fluid amplifiers for providinga hydraulic-pneumatic interface therebetween having no moving mechanical parts, the variable fluidicresis'tance means comprising a pair of analog-type fluid amplifiers disposed intermediate said first and second stage amplifiers, said pair of intermediate analog-type fluid amplifiers each comprising:

a power fluid inlet terminating in a nozzle;

a pair of control fluid inlets terminating in opposed nozzles; and

a vent downstream of said therewith.

2. The fluidic transducer set forth in claim 1 wherein a first control fluid inlet of a first of said intermediate fluid amplifiers in fluid communication with a first output of said first stage amplifier, and a first control fluid inlet of a second of said intermediate fluid amplifiers in fluid communication with a second output of said first stage amplifier. V

3. The fluidic transducer set forth in claim 2 wherein a second control fluid inlet of each of said pair of intermediate fluid amplifiers being blocked.

4. The fluidic transducer set forth in claim 3 wherein the power fluid inlet of each of said pair of intermediate fluid amplifiers in fluid communication with the power fluid supply of said second stage fluid amplifier.

5. The fluidic transducer set forth in claim 4 wherein a pair of fluidic resistors having equal fluid flow resistances are connected between the power fluid supply to said second stage amplifier and the power fluid inlets of said intermediate fluid power nozzle. and aligned r amplifiers.

6. The fluidic transducer set forth in claim 5 wherein the control fluid inlets of said second stage amplifier are connected to the junctures of the fluidic resistors and the power fluid inlets of said intermediate fluid amplifiers whereby a differentially pressurized input control signal of the first type fluid applied to the first stage amplifier produces unequal control of the downstream pressure of the power jets in the intermediate amplifiers to thereby reflect such unequal pressures into the control fluid inlets of the second stage amplifier wherein the magnitude of the reflected pressures is proportional to the magnitude of the input control signal.

7. The fluidic transducer set forth in claim 6 wherein said pair of intermediate analog-type fluid amplifiers are of identical construction and dimensions, and selected pressure relationships between the pressures of the power fluid supplied to the power fluid inlets of said first and second stages and intermediate amplifiers prevents undesired mixing of the pneumatic and hydraulic fluids.

8. The fluidic transducer set forth in claim 7 wherein said fluidic resistors have equal resistance values sufficient to provide a power fluid pressure to said intermediate amplifiers which is in the range of() to 0.40 of the power fluid pressure supplied to said second stage amplifier. 

